Results 1 to 6 of 6

Thread: DIY Line Output Converter W/ DSP Module

  1. #1
    Administrator
    Join Date
    Aug 2010
    Posts
    249

    DIY Line Output Converter W/ DSP Module

    I don't know if this falls in the low cost necessarily, but it is high value. Here is a complete module that operates as a line output converter (LOC), and a digital sound processor (DSP)

    The goal of this project was to build a unit that could convert the speaker level outputs of my stock head unit and supply a line level signal to a miniDSP module.

    http://www.minidsp.com/onlinestore/c...7/minidsp-kits

    Typical car audio branded LOCs generally have a limited bandwidth, and even within that bandwidth, the signal isn't very flat. All an LOC is is a group of small transformers that step down the voltage to a line level, and provide ground isolation. Since consumer car audio LOCs utilize such small, and inexpensive transformers, you'll get the limited bandwidth I was talking about. For example, David Navone brags that his LOCs exhibit bandwidth extending down to 80 hz. Roll off after that occurs at 12 db/oct, so by 20 hz, you're 24 db down in output. Usable, but we can do better, albeit with a considerably higher cost.

    Now in come the pro grade transformers. These are not cheap, but they exhibit a full audio bandwidth between 20-20khz, and the signal is flat. The most respected, and popular are made by a company called Jensen (not to be confused with Jensen Car Audio).

    http://www.jensen-transformers.com/

    I decided to use a JT-10KB-D transformer for this project based on a very simple schematic that Jensen provides on their website for a LOC. The schematic is listed under application AS068.

    http://www.jensen-transformers.com/apps_sc.html

    Since the power being supplied in this application is fairly small, it was very easy build. In fact, technically, you could just run this transformer without any additional resistors. I put some on the back purely for protection sake.



    Here are the transformers. You can fit about 4 transformers from a car audio branded LOC into one of these.



    Here's the input plug. Simply two runs of speaker wire, and a 12 volt power, and a ground wire.



    Output side.



    Total this project costs about $225.00. With another DSP module this could easily run a full 4-way setup for under $350.00.
    Last edited by MiniVanMan; 10-13-2010 at 02:02 AM.

  2. #2
    Founding Member TREETOP's Avatar
    Join Date
    Aug 2010
    Posts
    326
    I'm a sucker for just about anything that uses a project box and molex plugs.
    Well done!

    I'm starting to think a little harder about the miniDSP modules. It seems like I can't find an off-the-shelf head unit that'll keep me satisfied, and I don't have any interest in a CarPC. I'll be watching to see if you post more on the DSP module.

    It looks like the transformers each have 2 wires in and 4 wires out, why is that? And are they adjustable at all for input to output ratio?

  3. #3
    Administrator
    Join Date
    Aug 2010
    Posts
    249
    Thank you. Your earlier tutorial is what got me off my ass to take some pictures and post this.

    I was originally going to go with a carPC and even had it built. But the miniDSP modules came about, and just made things simpler, and cheaper. Anything that can help me keep the minivan, which is a company vehicle, as stock as possible is worth looking at for me.

    Take a look at the schematic for that transformer.



    The transformer can also be used for a balanced output as well. I'm running it unbalanced. There's a ground on both the input and output of the transformer, and the negative signal is also ran to ground on the output side. That would be ran to the center pin in a balanced configuration. Couple those with the speaker level inputs (+/-) and the positive output, and you have the six wires you see.

    It's a 4:1 stepdown, if you want something different, you need a different transformer. I figure at max output, I'll probably run about 2.5-3 volts, which will be about perfect for the miniDSP. You can add resistors in series if you want to dump even more voltage though. With only about 10-11 volts coming from the head unit, and low wattage, I'm running them straight. Nothing I can't go back in and mess with later though.

  4. #4
    Founding Member el_chupo_'s Avatar
    Join Date
    Aug 2010
    Location
    Cleburne, TX
    Posts
    128
    Real Name
    Matt
    For the sake of simplifying this even further for someone not familiar with some of the products and to point out this is not a $225 LOC.

    It appears you have the speaker wires going into the project box via the molex connecter -> to the transformers per the schematic above.
    Then the outputs are being ran (wired) to the ZN 5.0 (DIY) RCA plugs. This runs into one of the MiniDSP boards you have selected to use in your application.
    Then you have simply made a male ->female RCA cable with the female ends attached to the "output side" of the project box

    So essentially you have a created a 2-in-1 project in a single box. Correct?
    Last edited by el_chupo_; 08-28-2010 at 06:29 PM.

  5. #5
    Administrator
    Join Date
    Aug 2010
    Posts
    249
    That's exactly what I did.

  6. #6
    Junior Member
    Join Date
    Oct 2010
    Location
    Evansville, IN
    Posts
    2
    I'm definitely adept at DIY Audio, but the DSP side is where I get a little side-tracked...

    I have a P800PRS and it can do limited AutoEQ and Auto TA, but for now it's acceptable to me until I get the rest of the system together. As an interim step, I could feed the RCA outputs of my P800PRS through a resistor to knock the 4V down to 2V, then use the miniDSP to do a 4-way cross-over allow me to go active 3-ways up front with a sub and 2-way or coax in the rear, correct? A low cost interim step while I save for a MS-8?

    Which plug ins are you using?
    Last edited by BoilermakerFan; 10-27-2010 at 10:17 AM.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •